Increased intragraft rejection-associated gene transcripts in patients with donor-specific antibodies and normal biopsies

Predictors of graft failure after first detection of de novo donor-specific HLA antibodies in kidney transplant recipients

BACKGROUND

De novo donor-specific antibodies (dnDSAs) may cause antibody-mediated rejection and graft dysfunction. Little is known about the clinical course after first detection of dnDSAs during screening in asymptomatic patients. We aimed to assess the value of estimated glomerular filtration rate (eGFR) and proteinuria to predict graft failure in patients with dnDSAs and their potential utility as surrogate endpoints.

METHODS

All 400 kidney transplant recipients with dnDSAs at our centre (1 March 2000-31 May 2021) were included in this retrospective study. The dates of graft loss, rejection, doubling of creatinine, ≥30% eGFR decline, proteinuria ≥500 mg/g and ≥1000 mg/g were registered from the first dnDSA appearance.

RESULTS

During 8.3 years of follow-up, graft failure occurred in 33.3% of patients. Baseline eGFR and proteinuria correlated with 5-year graft loss (area under the receiver operating characteristics curve 0.75 and 0.80, P < .001). Creatinine doubled after a median of 2.8 years [interquartile range (IQR) 1.5-5.0] from dnDSA and the time from doubling creatinine to graft failure was 1.0 year (IQR 0.4-2.9). Analysing eGFR reduction ≥30% as a surrogate endpoint (148/400), the time from dnDSA to this event was 2.0 years (IQR 0.6-4.2), with a positive predictive value (PPV) of 45.9% to predict graft loss, which occurred after 2.0 years (IQR 0.8-3.2). The median time from proteinuria ≥500 mg/g and ≥1000 mg/g to graft failure was identical, 1.8 years, with a PPV of 43.8% and 49.0%, respectively. Composite endpoints did not improve PPV. Multivariable analysis showed that rejection was the most important independent risk factor for all renal endpoints and graft loss.

CONCLUSIONS

Renal function, proteinuria and rejection are strongly associated with graft failure in patients with dnDSA and may serve as surrogate endpoints.

Performance and Advancement of the Kidney Solid Organ Response Test

BACKGROUND

The kidney solid organ response test (kSORT) has been investigated for the prediction of acute rejection in kidney transplant recipients with conflicting results. We aimed to investigate if the kSORT assay score is associated with rejection or immune quiescence.

METHODS

The blinded association between rejection and kSORT > 9 were investigated. Optimization of kSORT prediction was evaluated after unblinding to determine the optimal prediction cutoff value of kSORT score. Additionally, the predictive capability of the kSORT gene set was assessed using blinded normalized gene expression data from microarray (Affymetrix) and qPCR assays.

RESULTS

Of the 95 blood samples analyzed, 18 patients had blood samples before transplant, 77 patients after transplant and 71 had clinically indicated biopsies of which 15 biopsies showed acute rejection and 16 showed chronic active antibody-mediated rejection. When 31 patients with rejection were compared to the remaining 64 patients, positive predictive value (PPV) was 54.29% and negative predictive value (NPV) was 75% when stratified using a kSORT score > 9, and PPV was 57.89% and NPV was 78.95% when stratified using a kSORT score > 5. Using the kSORT assay for detection of rejection showed an area under the curve value of 0.71. Microarray data improved prediction accuracy with PPV of 53% and NPV of 84% compared to qPCR results (PPV and NPV were 36% and 66%), respectively.

CONCLUSIONS

The kSORT assay has the potential to be used as a predictive tool for active rejection and/or immune quiescence, but additional studies will be useful in improving and refining the kSORT assay, in particular the prediction algorithm.

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

Utility of Banff Human Organ Transplant Gene Panel in Human Kidney Transplant Biopsies

BACKGROUND

Microarray transcript analysis of human renal transplantation biopsies has successfully identified the many patterns of graft rejection. To evaluate an alternative, this report tests whether gene expression from the Banff Human Organ Transplant (B-HOT) probe set panel, derived from validated microarrays, can identify the relevant allograft diagnoses directly from archival human renal transplant formalin-fixed paraffin-embedded biopsies. To test this hypothesis, principal components (PCs) of gene expressions were used to identify allograft diagnoses, to classify diagnoses, and to determine whether the PC data were rich enough to identify diagnostic subtypes by clustering, which are all needed if the B-HOT panel can substitute for microarrays.

METHODS

RNA was isolated from routine, archival formalin-fixed paraffin-embedded tissue renal biopsy cores with both rejection and nonrejection diagnoses. The B-HOT panel expression of 770 genes was analyzed by PCs, which were then tested to determine their ability to identify diagnoses.

RESULTS

PCs of microarray gene sets identified the Banff categories of renal allograft diagnoses, modeled well the aggregate diagnoses, showing a similar correspondence with the pathologic diagnoses as microarrays. Clustering of the PCs identified diagnostic subtypes including non-chronic antibody-mediated rejection with high endothelial expression. PCs of cell types and pathways identified new mechanistic patterns including differential expression of B and plasma cells.

CONCLUSIONS

Using PCs of gene expression from the B-Hot panel confirms the utility of the B-HOT panel to identify allograft diagnoses and is similar to microarrays. The B-HOT panel will accelerate and expand transcript analysis and will be useful for longitudinal and outcome studies.

Phosphorylation of S6RP in peritubular capillaries of kidney grafts and circulating HLA donor-specific antibodies

Antibody-mediated rejection (ABMR) caused by donor-specific HLA-antibodies (DSA) is a mediator of allograft loss after kidney transplantation (KT). DSA can activate microvascular endothelium damage through the mTOR pathway. In this study we assessed the mTOR pathway activation by DSA in KT with ABMR (ABMR + DSA+) compared to controls (ABMR−DSA−), biopsies with ABMR changes without DSA (ABMR + DSA−) and DSA without ABMR changes (ABMR−DSA+), and the potential modulation by mTOR inhibitors (mTORi). We evaluated 97 biopsies: 31 ABMR + DSA+, 33 controls ABMR-DSA−, 16 ABMR + DSA−, and 17 ABMR-DSA+ cases. Regarding immunosuppression of full ABMR + DSA+ and controls, 21 biopsies were performed under mTORi treatment (11 of them ABMR + DSA+ cases) and 43 without mTORi (20 of them ABMR + DSA+) so as to explore its effect on the mTOR pathway. Biopsies were stained for C4d, Ki67, and phosphorylated (p) S6RP, ERK, and mTOR by immunohistochemistry. Labeling was graded according to peritubular capillary staining. ABMR biopsies showed significantly higher C4d, p-S6RP, and Ki67 staining in peritubular capillaries (PTC) compared to controls, and light differences in p-ERK or p-mTOR. mTORi treatment did not modify p-S6RP, p-mTOR, and p-ERK staining. Diffuse p-S6RP in PTC in the biopsies significantly associated with circulating HLA-DSA independently of graft rejection, and with worse death-censored graft survival. These findings suggest that activation of endothelium through the mTOR pathway evidence different mechanisms of damage in ABMR + DSA+ and ABMR + DSA− despite similar histological injury.

The Presence of Donor-specific Antibodies Around the Time of Pancreas Graft Biopsy With Rejection Is Associated With an Increased Risk of Graft Failure

BACKGROUND

Donor-specific antibodies (DSA) against HLA are an important biomarker predicting graft injury, rejection (Rej), and failure in various solid-organ transplant recipients. However, the impact of DSA with or without histopathological evidence of rejection among pancreas transplant recipients (PTRs) is unknown.

METHODS

In this study, we included all PTRs at our center between 2005 and 2020, with pancreas allograft biopsy before March 31, 2021, and with DSA checked within 15 d of the biopsy. PTRs were divided into 4 groups based on the biopsy findings on the index biopsy and DSA status as Rej-/DSA-, Rej+/DSA-, Rej-/DSA+, and Rej+/DSA+.

RESULTS

Two hundred two PTRs had a pancreas allograft biopsy during the study period. Thirty-nine were in Rej-/DSA-, 84 Rej+/DSA-, 24 Rej-/DSA+, and 55 Rej+/DSA+. The mean interval from transplant to index biopsy was not statistically different between the 4 groups. The most common type of rejection was T cell-mediated rejection; however, antibody-mediated rejection was more prevalent in the Rej+/DSA+ group. At 5 y postbiopsy, the rate of death-censored graft failure (DCGF) for Rej-/DSA- was 18%, 24% in Rej+/DSA-; 17% in Rej-/DSA+ and 36% in Rej+/DSA+ (P = 0.14). In univariate analysis, mixed rejection (hazard ratio [HR], 3.0; 95% confidence intervals [CI], 1.22-7.39; P = 0.02) along with solitary pancreas transplantation and Rej+/DSA+ were associated with DCGF. In multivariate analysis, compared with Rej-/DSA-, Rej+/DSA+ was significantly associated with DCGF (HR, 2.32; 95% CI, 1.03-5.20; P = 0.04); however, Rej+/DSA- was not (HR, 1.06; 95% CI, 0.32-3.56; P = 0.92).

CONCLUSIONS

PTRs with pancreas allograft rejection and concomitant DSA have an increased risk of DCGF.

Circulating Donor-Specific Anti-HLA Antibodies Associate With Immune Activation Independent of Kidney Transplant Histopathological Findings

Despite the critical role of cytokines in allograft rejection, the relation of peripheral blood cytokine profiles to clinical kidney transplant rejection has not been fully elucidated. We assessed 28 cytokines through multiplex assay in 293 blood samples from kidney transplant recipients at time of graft dysfunction. Unsupervised hierarchical clustering identified a subset of patients with increased pro-inflammatory cytokine levels. This patient subset was hallmarked by a high prevalence (75%) of donor-specific anti-human leukocyte antigen antibodies (HLA-DSA) and histological rejection (70%) and had worse graft survival compared to the group with low cytokine levels (HLA-DSA in 1.7% and rejection in 33.7%). Thirty percent of patients with high pro-inflammatory cytokine levels and HLA-DSA did not have histological rejection. Exploring the cellular origin of these cytokines, we found a corresponding expression in endothelial cells, monocytes, and natural killer cells in single-cell RNASeq data from kidney transplant biopsies. Finally, we confirmed secretion of these cytokines in HLA-DSA-mediated cross talk between endothelial cells, NK cells, and monocytes. In conclusion, blood pro-inflammatory cytokines are increased in kidney transplant patients with HLA-DSA, even in the absence of histology of rejection. These observations challenge the concept that histology is the gold standard for identification of ongoing allo-immune activation after transplantation.

Diagnostic application of transcripts associated with antibody-mediated rejection in kidney transplant biopsies

Background

The diagnosis of antibody-mediated rejection (AMR) is reached using the Banff Classification for Allograft Pathology, which now includes gene expression analysis. In this study, we investigate the application of ‘increased expression of thoroughly validated gene transcripts/classifiers strongly associated with AMR’ as diagnostic criteria.

Method

We used quantitative real-time polymerase chain reaction for 10 genes associated with AMR in a retrospective cohort of 297 transplant biopsies, including biopsies that met the full diagnostic criteria for AMR, even without molecular data (AMR, n = 27), biopsies that showed features of AMR, but that would only meet criteria for AMR with increased transcripts [suspicious for AMR (AMRsusp), n = 49] and biopsies that would never meet criteria for AMR (No-AMR, n = 221).

Results

A 10-gene AMR score trained by a receiver-operating characteristic to identify AMR found 16 cases with a high score among the AMRsusp cases (AMRsusp-high) that had significantly worse graft survival than those with a low score (AMRsusp-low; n = 33). In both univariate and multivariate Cox regression analysis, the AMR 10-gene score was significantly associated with an increased hazard ratio (HR) for graft loss (GL) in the AMRsusp group (HR = 1.109, P = 0.004 and HR = 1.138, P = 0.012, respectively), but not in the whole cohort. Net reclassification index and integrated discrimination improvement analyses demonstrated improved risk classification and superior discrimination, respectively, for GL when considering the gene score in addition to histological and serological data, but only in the AMRsusp group, not the whole cohort.

Conclusions

This study provides evidence that a gene score strongly associated with AMR helps identify cases at higher risk of GL in biopsies that are suspicious for AMR but do not meet full criteria.

Inflammation Determines the Capacity of Allogenic Endothelial Cells to Regulate Human Treg Expansion

During allotransplantation, the endothelium acts as semi-professional antigen-presenting cells with the ability to activate proliferation and to promote differentiation of CD4⁺-T subsets. These abilities are dependent on the luminal expression of HLA class II antigens by microvascular endothelial cells, which is regulated by inflammatory cytokines. The upregulation of HLA-DR and HLA-DQ during rejection implies significant intragraft inflammation. Furthermore, the microvascular inflammation is an independent determinant for renal allograft failure. In this study, the potential of inflammation to modify endothelial regulation of peripheral CD4⁺ Treg cells was examined. Microvascular endothelial cells were exposed to pro-inflammatory cytokines for varying durations before co-culture with PBMC from non-HLA matched donors. Proliferation and expansion of CD4⁺Treg and soluble factor secretion was determined. Early interactions were detected by phosphorylation of Akt. Video microscopy was used to examine spatial and temporal endothelial-CD4⁺T interactions. Highly inflammatory conditions led to increased endothelial expression of HLA-DR, the adhesion molecule ICAM-1, the costimulatory molecule PD-L1 and de novo expression of HLA-DQ. Treg differentiation was impaired by exposure of endothelial cells to a high level of inflammation. Neither IL-6, IL-2 nor TGFβ were implicated in reducing Treg numbers. High PD-L1 expression interfered with early endothelial cell interactions with CD4⁺T lymphocytes and led to modified TCR signaling. Blocking endothelial PD-L1 resulted in a partial restoration of Treg. The allogenic endothelial cell-mediated expansion of Treg depends on a critical threshold of inflammation. Manipulation of the PD-L1/PD-1 pathway or endothelial activation post-transplantation may promote or interfere with this intrinsic mechanism of allospecific Treg expansion.

The immunohistochemical expression of von Willebrand factor, T-cadherin, and Caveolin-1 is increased in kidney allograft biopsies with antibody-mediated injury

BACKGROUND

There are only a few reports evaluating the applicability of endothelial-damage markers analysis by immunohistochemistry (IHC) in kidney allograft samples. This study analyzed the expression of Caveolin-1 (Cav), von Willebrand factor (Vwf), and T-cadherin (Cad) in kidney biopsies and their association with antibody-mediated injury.

METHODS

In this retrospective study, 114 cases with antibody-mediated changes (Banff, 2020) and 72 with interstitial fibrosis/tubular atrophy were selected. IHC for Cav, Vwf and Cad was performed and evaluated according to their qualitative expression in peritubular capillaries. The cases were grouped according to the presence of microvascular inflammation (MVI), donor-specific antibodies (DSA), C4d positivity and antibody-mediated rejection (AMR). A level of significance < 0.05 was adopted.

RESULTS

Vwf expression was associated with MVI (p < 0.001), DSA (p = 0.016), C4d (p < 0.001) and AMR (p < 0.001), and was higher in DSA+/C4d+ cases despite MVI (p < 0.001). The expression of Cad correlated with MVI (p = 0.015), C4d (p = 0.005) and AMR (p = < 0.001). Cad was more expressed in chronic AMR compared with acute/active cases (p = 0.001). Cav expression was associated with MVI (p = 0.029) and AMR (p = 0.016) and was also higher in chronic AMR (p = 0.049). A combined score of Vwf and Cad was higher in AMR when compared with C4d without rejection and IF/TA cases (p < 0.001).

CONCLUSION

Vwf, Cad and Cav expression shows association with antibody-mediated injury and may be helpful to support AMR diagnosis.

Technical considerations when designing a gene expression panel for renal transplant diagnosis

Gene expression analysis is emerging as a new diagnostic tool in transplant pathology, in particular for the diagnosis of antibody-mediated rejection. Diagnostic gene expression panels are defined on the basis of their pathophysiological relevance, but also need to be tested for their robustness across different preservatives and analysis platforms. The aim of this study is the investigate the effect of tissue sampling and preservation on candidate genes included in a renal transplant diagnostic panel. Using the NanoString platform, we compared the expression of 219 genes in 51 samples, split for formalin-fixation and paraffin-embedding (FFPE) and RNAlater preservation (RNAlater). We found that overall, gene expression significantly correlated between FFPE and RNAlater samples. However, at the individual gene level, 46 of the 219 genes did not correlate across the 51 matched FFPE and RNAlater samples. Comparing gene expression results using NanoString and qRT-PCR for 18 genes in the same pool of RNA (RNAlater), we found a significant correlation in 17/18 genes. Our study indicates that, in samples from the same routine diagnostic renal transplant biopsy procedure split for FFPE and RNAlater, 21% of 219 genes of potential biological significance do not correlate in expression. Whether this is due to fixatives or tissue sampling, selection of gene panels for routine diagnosis should take this information into consideration.

Key driver genes as potential therapeutic targets in renal allograft rejection

Acute rejection (AR) in renal transplantation is an established risk factor for reduced allograft survival. Molecules with regulatory control among immune pathways of AR that are inadequately suppressed, despite standard-of-care immunosuppression, could serve as important targets for therapeutic manipulation to prevent rejection. Here, an integrative, network-based computational strategy incorporating gene expression and genotype data of human renal allograft biopsy tissue was applied, to identify the master regulators - the key driver genes (KDGs) - within dysregulated AR pathways. A 982-meta-gene signature with differential expression in AR versus non-AR was identified from a meta-analysis of microarray data from 735 human kidney allograft biopsy samples across 7 data sets. Fourteen KDGs were derived from this signature. Interrogation of 2 publicly available databases identified compounds with predicted efficacy against individual KDGs or a key driver-based gene set, respectively, which could be repurposed for AR prevention. Minocycline, a tetracycline antibiotic, was chosen for experimental validation in a murine cardiac allograft model of AR. Minocycline attenuated the inflammatory profile of AR compared with controls and when coadministered with immunosuppression prolonged graft survival. This study demonstrates that a network-based strategy, using expression and genotype data to predict KDGs, assists target prioritization for therapeutics in renal allograft rejection.

HLA-DQ alloantibodies directly activate the endothelium and compromise differentiation of FoxP3high regulatory T lymphocytes

Development of donor-specific antibodies is associated with reduced allograft survival in renal transplantation. Recent clinical studies highlight the prevalence of human leukocyte antigen (HLA)-DQ antibodies amongst de novo donor-specific antibodies (DSAs), yet the specific contribution of these DSAs to rejection has not been examined. Antibody-mediated rejection primarily targets the microvasculature, so this study explored how patient HLA-DQ alloantibodies can modulate endothelial activation and so immunoregulation. HLA-DQ antibodies phosphorylated Akt and S6 kinase in microvascular endothelial cells. This activation prior to culture with alloreactive lymphocytes increased IL-6 and RANTES secretion. The antibody-mediated upregulation of IL-6 was indeed Akt-dependent. The binding of HLA-DQ antibodies to endothelial cells selectively reduced T cell alloproliferation and FoxP3^high Treg differentiation. In clinical studies, detection of HLA-DQ DSAs with other DSAs is associated with worse graft survival than either alone. Endothelial cells stimulated with HLA-DR and HLA-DQ antibodies showed a synergistic increase in pro-inflammatory cytokine secretion and a decrease in Treg expansion. HLA-DQ antibodies strongly promote pro-inflammatory responses in isolation and in combination with other HLA antibodies. Thus, our data give new insights into the pathogenicity of HLA-DQ DSAs.

Donor-Specific Antibodies in the Absence of Rejection Are Not a Risk Factor for Allograft Failure

Introduction

Donor-specific antibodies (DSAs) are considered an important risk factor for graft injury and failure. However, there is limited information on long-term outcomes for kidney transplant recipients with positive DSAs in the absence of rejection on biopsy.

Methods

We evaluated all patients at the University of Wisconsin who underwent a kidney allograft biopsy between January 1, 2013, and December 31, 2016. All patients with clinical indication or protocol biopsies that were negative for acute rejection and lacked significant acute pathological features were included in the study and divided into 2 groups based on DSAs at the time of biopsy. There were a total of 1102 kidney biopsies during the study period of which 587 fulfilled our selection criteria (DSA+, n = 192, and DSA−, n = 395). The incidence of subsequent rejection and death-censored graft failure (DCGF) were outcomes of interest.

Results

There was no difference in acute (i + t + v + c4d + ptc + g = 0 in both groups) or chronic (ci + ct + cv + cg = 2.4 ± 2.2 vs. 2.7 ± 2.4; cg = 0.12 ± 0.48 vs. 0.13 ± 0.48) Banff scores in the index biopsy. Patients were followed for a mean of 33.1 ± 16.8 months. Kaplan-Meier analyses demonstrated a higher incidence of DCGF in DSA− group (n = 83) but this was not observed for subsequent rejection (n = 76). In multivariate Cox regression analyses, the interval from transplant to biopsy, de novo DSA, and younger age remained independently associated with increased risk of subsequent rejection. Notably, there was no association between subsequent rejection or DSA (pretransplant, de novo, persistant, Class I/II, MFI_sum, or MFI_max) and graft failure.

Conclusion

This study suggests that in the absence of biopsy-proven rejection and acute inflammation, human leukocyte antigen (HLA) DSAs are not associated with increased risk of graft failure.

Molecular signatures and clinical outcomes of transplant glomerulopathy stratified by microvascular inflammation and donor-specific antibody

BACKGROUND

We investigated clinical outcomes and molecular signatures of transplant glomerulopathy (TG) stratified by microvascular inflammation (MVI) and donor-specific antibody (DSA) status.

METHODS

We performed a retrospective review of 749 kidney transplant patients who received a for-cause kidney biopsy from 2009 to 2014. We classified TG as MVI positive (MVI+) or MVI negative (MVI-), and with or without DSA. We obtained gene expression profiles for 44 biopsies by Affymetrix HuGene 1.0 ST expression arrays.

RESULTS

A total of 100 patients had TG; 49 were MVI+, and 51 were MVI-. After a median post-biopsy follow-up of 2.08 years (range 0.43-4.59), Kaplan-Meier survival analysis demonstrated worse allograft survival in MVI+ TG patients compared with MVI- TG patients (P = 0.01), and time to graft failure was significantly shorter in MVI+ patients (1.08 ± 1.01 years vs 2.3 ± 1.8 years; P = 0.002). DSA status did not affect graft survival within MVI+ or MVI- groups. Analysis of pathogenesis-based transcripts (PBT) showed that MVI+ TG biopsies had increased expression of gamma interferon and rejection (GRIT) and DSA-associated transcripts (DSAST), as observed in antibody-mediated rejection. MVI- TG biopsies had increased expression of cytotoxic and regulatory T cell- and B cell-associated transcripts but not GRIT or DSAST. DSA status had no effect on expression of any PBTs studied in MVI- TG biopsies.

CONCLUSIONS

Graft survival in TG is significantly worse in the presence of MVI. Gene expression profiles of MVI+ TG resemble antibody-mediated rejection while gene expression profiles of MVI- TG resemble cell-mediated rejection regardless of DSA status.

The Banff 2017 Kidney Meeting Report: Revised diagnostic criteria for chronic active T cell-mediated rejection, antibody-mediated rejection, and prospects for integrative endpoints for next-generation clinical trials

The kidney sessions of the 2017 Banff Conference focused on 2 areas: clinical implications of inflammation in areas of interstitial fibrosis and tubular atrophy (i-IFTA) and its relationship to T cell-mediated rejection (TCMR), and the continued evolution of molecular diagnostics, particularly in the diagnosis of antibody-mediated rejection (ABMR). In confirmation of previous studies, it was independently demonstrated by 2 groups that i-IFTA is associated with reduced graft survival. Furthermore, these groups presented that i-IFTA, particularly when involving >25% of sclerotic cortex in association with tubulitis, is often a sequela of acute TCMR in association with underimmunosuppression. The classification was thus revised to include moderate i-IFTA plus moderate or severe tubulitis as diagnostic of chronic active TCMR. Other studies demonstrated that certain molecular classifiers improve diagnosis of ABMR beyond what is possible with histology, C4d, and detection of donor-specific antibodies (DSAs) and that both C4d and validated molecular assays can serve as potential alternatives and/or complements to DSAs in the diagnosis of ABMR. The Banff ABMR criteria are thus updated to include these alternatives. Finally, the present report paves the way for the Banff scheme to be part of an integrative approach for defining surrogate endpoints in next-generation clinical trials.

Clinically relevant interpretation of solid phase assays for HLA antibody

Purpose of review

Accurate and timely detection and characterization of human leukocyte antigen (HLA) antibodies are critical for pre-transplant and post-transplant immunological risk assessment. Solid phase immunoassays have provided increased sensitivity and specificity, but test interpretation is not always straightforward. This review will discuss the result interpretation considering technical limitations; assessment of relative antibody strength; and the integration of data for risk stratification from complementary testing and the patient's immunological history.

Recent findings

Laboratory and clinical studies have provided insight into causes of test failures – false positive reactions because of antibodies to denatured HLA antigens and false negative reactions resulting from test interference and/or loss of native epitopes. Test modifications permit detection of complement-binding antibodies and determination of the IgG subclasses. The high degree of specificity of single antigen solid phase immunoassays has revealed the complexity and clinical relevance of antibodies to HLA-C, HLA-DQ, and HLA-DP antigens. Determination of antibody specificity for HLA epitopes enables identification of incompatible antigens not included in test kits.

Summary

Detection and characterization of HLA antibodies with solid phase immunoassays has led to increased understanding of the role of those antibodies in graft rejection, improved treatment of antibody-mediated rejection, and increased opportunities for transplantation. However, realization of these benefits requires careful and accurate interpretation of test results.

Defining the phenotype of antibody-mediated rejection in kidney transplantation: Advances in diagnosis of antibody injury

The diagnostic criteria for antibody-mediated rejection (ABMR) are constantly evolving in light of the evidence. Inclusion of C4d-negative ABMR has been one of the major advances in the Banff Classification in recent years. Currently Banff 2015 classification requires evidence of donor specific antibodies (DSA), interaction between DSA and the endothelium, and acute tissue injury (in the form of microvasculature injury (MVI); acute thrombotic microangiopathy; or acute tubular injury in the absence of other apparent cause). In this article we review not only the ABMR phenotypes acknowledged in the most recent Banff classification, but also the phenotypes related to novel pathogenic antibodies (non-HLA DSA, antibody isoforms and subclasses, complement-binding functionality) and molecular diagnostic tools (gene transcripts, metabolites, small proteins, cytokines, and donor-derived cell-free DNA). These novel tools are also being considered for the prognosis and monitoring of treatment response. We propose that improved classification of ABMR based on underlying pathogenic mechanisms and outcomes will be an important step in identifying patient-centered therapies to extend graft survival.

Increased Circulating T Lymphocytes Expressing HLA-DR in Kidney Transplant Recipients with Microcirculation Inflammation

We consecutively enrolled 82 kidney transplant recipients (KTRs) with stable renal function and 24 KTRs who underwent indication biopsy to compare the histological grading of renal allografts with the activity of circulating T lymphocyte subsets and monocytes determined by flow cytometry, which were obtained at 2 weeks after kidney transplantation (KT) and at the time of indication biopsy, respectively. The sum of the scores of glomerulitis (g) + peritubular capillaritis (ptc), inflammation (i) + tubulitis (t), interstitial fibrosis (ci) + tubular atrophy (ct), and fibrointimal thickening (cv) + arteriolar hyaline thickening (ah) was used to assign a histological grade to the renal allograft samples. The frequencies of CD4⁺HLA-DR⁺/CD4⁺ T cells and CD8⁺HLA-DR⁺/CD8⁺ T cells were significantly increased in KTRs with a microcirculation inflammation (MI) sum score ≥ 1 when compared with KTRs with an MI sum score = 0 as well as stable KTRs. In these 2 subsets, only CD4⁺HLA-DR⁺/CD4⁺ T cells were positively correlated with MI sum scores. Analysis using the receiver operating characteristic (ROC) curve showed that antibody-mediated rejection (AMR) could be predicted with a sensitivity of 80.0% and a specificity of 94.7%, using a cutoff value of 29.6% frequency of CD4⁺HLA-DR⁺/CD4⁺ T cells. MI was significantly associated with an increased frequency of activated T lymphocytes expressing human leukocyte antigen-antigen D related (HLA-DR). Further studies should focus on validating the utility of circulating CD4⁺HLA-DR⁺/CD4⁺ T cells as a noninvasive, immunologic monitoring tool for the prediction of AMR.

The Banff 2015 Kidney Meeting Report: Current Challenges in Rejection Classification and Prospects for Adopting Molecular Pathology

The XIII Banff meeting, held in conjunction the Canadian Society of Transplantation in Vancouver, Canada, reviewed the clinical impact of updates of C4d-negative antibody-mediated rejection (ABMR) from the 2013 meeting, reports from active Banff Working Groups, the relationships of donor-specific antibody tests (anti-HLA and non-HLA) with transplant histopathology, and questions of molecular transplant diagnostics. The use of transcriptome gene sets, their resultant diagnostic classifiers, or common key genes to supplement the diagnosis and classification of rejection requires further consensus agreement and validation in biopsies. Newly introduced concepts include the i-IFTA score, comprising inflammation within areas of fibrosis and atrophy and acceptance of transplant arteriolopathy within the descriptions of chronic active T cell-mediated rejection (TCMR) or chronic ABMR. The pattern of mixed TCMR and ABMR was increasingly recognized. This report also includes improved definitions of TCMR and ABMR in pancreas transplants with specification of vascular lesions and prospects for defining a vascularized composite allograft rejection classification. The goal of the Banff process is ongoing integration of advances in histologic, serologic, and molecular diagnostic techniques to produce a consensus-based reporting system that offers precise composite scores, accurate routine diagnostics, and applicability to next-generation clinical trials.

The Impact of HLA Class I-Specific Killer Cell Immunoglobulin-Like Receptors on Antibody-Dependent Natural Killer Cell-Mediated Cytotoxicity and Organ Allograft Rejection

Natural killer (NK) cells of the innate immune system are cytotoxic lymphocytes that play an important roles following transplantation of solid organs and hematopoietic stem cells. Recognition of self-human leukocyte antigen (HLA) class I molecules by inhibitory killer cell immunoglobulin-like receptors (KIRs) is involved in the calibration of NK cell effector capacities during the developmental stage, allowing the subsequent recognition and elimination of target cells with decreased expression of self-HLA class I (due to virus infection or tumor transformation) or HLA class I disparities (in the setting of allogeneic transplantation). NK cells expressing an inhibitory KIR-binding self-HLA can be activated when confronted with allografts lacking a ligand for the inhibitory receptor. Following the response of the adaptive immune system, NK cells can further destroy allograft endothelium by antibody-dependent cell-mediated cytotoxicity (ADCC), triggered through cross-linking of the CD16 Fc receptor by donor-specific antibodies bound to allograft. Upon recognizing allogeneic target cells, NK cells also secrete cytokines and chemokines that drive maturation of dendritic cells to promote cellular and humoral adaptive immune responses against the allograft. The cumulative activating and inhibitory signals generated by ligation of the receptors regulates mature NK cell killing of target cells and their production of cytokines and chemokines. This review summarizes the role of NK cells in allograft rejection and proposes mechanistic concepts that indicate a prominent role for KIR-HLA interactions in facilitating NK cells for Fc receptor-mediated ADCC effector function involved in antibody-mediated rejection of solid organ transplants.

Cellular and molecular profiling of graft injury post renal transplantation

PURPOSE OF REVIEW

Continues advancements in assessing methods for biomolecules that have assisted to identify surrogate candidate biomarkers that can be used to monitor the transplanted organ. These high-throughput methods can help researchers to significantly speed up the identification and the validation steps, which are crucial factors for biomarker discovery efforts. However, this task in transplantation confronts multiple limitations. The review summarizes main findings using 'omics approaches in the evaluation of different types of allograft injury with the overarching aim of evaluating the next steps for transferring the available data to the clinical setting.

RECENT FINDINGS

Significant discoveries have been made about the molecular and cellular mechanisms that associate with graft injury that may lead to early biomarkers of graft injury (prediction and diagnosis) with the goal of improving long-term outcomes by extending the lifespan of the graft and/or identifying new therapeutic targets.

SUMMARY

Common efforts among researchers are needed for transferring biomarkers to the clinical setting and, moreover, elucidate pathways that may allow for early interventions to avoid fibrosis progression and graft loss. Large and prospective studies for validation of current available data under strict analytical evaluation are needed to move biomarkers from the discovery phase to validation and clinical implementation.

Surveillance biopsies after paediatric kidney transplantation: A review

Kidney transplantation is the most effective means of treating children with end-stage kidney disease, and yet, there continues to be a limited "life span" of transplanted kidneys in paediatric recipients. Early graft monitoring, using the surveillance biopsy, has the potential to extend renal allograft survival in paediatric recipients. The surveillance biopsy provides important and timely information about acute and chronic graft pathology, particularly SCR and calcineurin inhibitor-induced nephrotoxicity, which can subsequently guide management decisions and improve long-term graft survival. The ostensible value of the surveillance biopsy is furthered by the limitations of conventional renal functional studies. However, there is still much debate surrounding the surveillance biopsy in paediatric recipients, particularly in regard to its overall utility, safety and timing. This review discusses the current literature regarding the utility, safety, and potential predictive value of surveillance biopsies for guiding post-transplant management in paediatric renal allograft recipients, as well as the viability of other potentially newer non-invasive strategies for renal allograft monitoring.

HLA Class II Antibody Activation of Endothelial Cells Promotes Th17 and Disrupts Regulatory T Lymphocyte Expansion

Kidney transplantation is the most successful treatment option for patients with end-stage renal disease, and chronic antibody-mediated rejection is the principal cause of allograft loss. Predictive factors for chronic rejection include high levels of HLA alloantibodies (particularly HLA class II) and activation of graft endothelial cells (ECs). The mechanistic basis for this association is unresolved. We used an experimental model of HLA-DR antibody stimulation of microvascular ECs to examine the mechanisms underlying the association between HLA class II antibodies, EC activation and allograft damage. Activation of ECs with the F(Ab')2 fragment of HLA-DR antibody led to phosphorylation of Akt, ERK and MEK and increased IL-6 production by ECs cocultured with allogeneic peripheral blood mononuclear cells (PBMCs) in an Akt-dependent manner. We previously showed that HLA-DR-expressing ECs induce polarization of Th17 and FoxP3(bright) regulatory T cell (Treg) subsets. Preactivation of ECs with anti-HLA-DR antibody redirected EC allogenicity toward a proinflammatory response by decreasing amplification of functional Treg and by further increasing IL-6-dependent Th17 expansion. Alloimmunized patient serum containing relevant HLA-DR alloantibodies selectively bound and increased EC secretion of IL-6 in cocultures with PBMCs. These data contribute to understanding of potential mechanisms of antibody-mediated endothelial damage independent of complement activation and FcR-expressing effector cells.

The Role of Natural Killer Cells in Humoral Rejection

Antibody-mediated rejection (AMR) has been identified among the most important factors limiting long-term outcome in cardiac and renal transplantation. Therapeutic management remains challenging and the development of effective treatment modalities is hampered by insufficient understanding of the underlying pathophysiology. However, recent findings indicate that in addition to AMR-triggered activation of the classical complement pathway, antibody-dependent cellular cytotoxicity by innate immune cell subsets also promotes vascular graft injury. This review summarizes the accumulating evidence for the contribution of natural killer cells, the key mediators of antibody-dependent cellular cytotoxicity, to human AMR in allotransplantation and xenotransplantation and illustrates the current mechanistic conceptions drawn from animal models.

Donor Specific Antibodies are not only directed against HLA-DR: Minding your Ps and Qs

During solid organ transplantation, interactions between recipient and donor immune cells occur chiefly in the allograft microvasculature. All three HLA class II antigens, DR, DP and DQ, have been detected on renal EC with a markedly increased expression of HLA class II observed in renal allografts undergoing rejection. Recent studies of donor-specific antibodies (DSA) have exposed the prevalence of de novo DSA directed against HLA-DQ, as well as a strong association between these antibodies and allograft damage. The HLA-DQ molecule can be distinguished from the other class II antigens by its transcription, expression and peptide repertoire. The distinct intragraft expression and immunogenicity of HLA-DQ may contribute to the incidence of HLA-DQ DSA, as well as directing the DSA-mediated damage. The possibility of HLA class II antigen-specific signaling in EC may reveal different mechanisms of allograft damage that act in tandem with complement-dependent injury. This review addresses the features of the HLA-DQ heterodimer that may underlie the high incidence of HLA-DQ directed DSA and their association with allograft damage. We also consider existing data in hematopoietic stem cell transplantation concerning HLA directed DSA.

The prevalence and clinical significance of C1q-binding donor-specific anti-HLA antibodies early and late after kidney transplantation

We aimed to determine the prevalence and clinical significance of complement-binding donor-specific antibodies (DSA) detected up to 30 years after kidney transplantation. Group 1 patients included 284 consecutive DSA negative patients who underwent kidney transplantation after 1 May 2009. Group 2 included 405 patients transplanted before this date and followed at our center with functioning allografts. DSA were tested using Luminex Single Antigen and the C1q assay. In Group 1 patients, who were monitored prospectively, 31 (11%) developed de novo DSA during a median follow-up of 2.5 (1.9, 3.6) years. Of these, 11 (4%) had C1q+ and 20 (7%) had C1q negative DSA. In Group 2 patients, 77 (19%) displayed DSA. Among these, 33 (8%) had C1q+ and 44 (11%) had C1q negative DSA. The incidence of acute antibody-mediated rejection (AMR) was significantly higher in C1q+DSA patients in both Group 1 (45%) and Group 2 (15%) compared with C1q negative DSA (5% and 2%) and DSA negative patients (1% and 3%; P < 0.001 and P = 0.001). The incidence of chronic AMR was 36% (Group 1) and 51% (Group 2) in patients with C1q+DSA. In contrast, chronic AMR occurred in 5% and 25% of C1q negative DSA, and 2% and 6% of DSA negative Group 1 and 2 patients, respectively (P < 0.001). Although the graft survival was lower in Group 1 C1q+DSA patients (73%) compared with C1q negative DSA (95%) and DSA negative (94%) patients, the difference was not statistically significant by Kaplan-Meier survival analysis (P = 0.21). Our results indicated that the presence of C1q+ DSA was associated with acute and chronic AMR.

Tubuloreticular Inclusions in Renal Allografts Associate with Viral Infections and Donor-Specific Antibodies

The presence of tubuloreticular inclusions (TRIs) in native glomerular endothelial cells associates with viral infections and lupus nephritis. However, the associations of TRIs in renal transplant biopsy specimens are not known. We analyzed data from 316 patients who had a transplant biopsy with electron microscopy examination; 41 of 316 (13.0%) patients had TRIs. Patients with TRIs had significantly lower allograft survival rates (50.9%) than patients without TRIs (74.3%; P=0.03). Transplant glomerulopathy-free survival was also inferior in the TRI-positive group (57.5%) compared with the TRI-negative group (87.3%; P=0.002). Serologically, hepatitis C associated with the presence of TRIs (P=0.04) along with donor-specific antibodies (P=0.01). Furthermore, patients who were TRI positive were more likely than patients who were TRI negative to have had a previous rejection episode (P=0.02). On multivariate analysis, TRIs associated with prior rejection, viral infections, and class 1 HLA donor-specific antibodies. These results show that the presence of TRIs in renal allograft biopsy specimens associates with poor allograft outcomes and serologic evidence of viral infections and alloimmunity. The association with alloimmunity is a novel finding that warrants additional investigation.

Use of Quantitative Real Time Polymerase Chain Reaction to Assess Gene Transcripts Associated With Antibody-Mediated Rejection of Kidney Transplants

INTRODUCTION

Microarray studies have shown elevated transcript levels of endothelial and natural killer (NK) cell-associated genes during antibody-mediated rejection (AMR) of the renal allograft. This study aimed to assess the use of quantitative real-time polymerase chain reaction as an alternative to microarray analysis on a subset of these elevated genes.

METHODS

Thirty-nine renal transplant biopsies from patients with de novo donor-specific antibodies and eighteen 1-year surveillance biopsies with no histological evidence of rejection were analyzed for expression of 11 genes previously identified as elevated in AMR.

RESULTS

Expression levels of natural killer markers were correlated to microcirculation inflammation and graft outcomes to a greater extent than endothelial markers. Creating a predictive model reduced the number of gene transcripts to be assessed to 2, SH2D1b and MYBL1, resulting in 66.7% sensitivity and 89.7% specificity for graft loss.

DISCUSSION

This work demonstrates that elevated gene expression levels, proposed to be associated with AMR, can be detected by established quantitative real-time polymerase chain reaction technology, making transition to the clinical setting feasible. Transcript analysis provides additional diagnostic information to the classification schema for AMR diagnosis but it remains to be determined whether significant numbers of centres will validate transcript analysis in their laboratories and put such analysis into clinical use.

Transplant biopsy beyond light microscopy

Despite its long-standing status as the diagnostic "gold standard", the renal transplant biopsy is limited by a fundamental dependence on descriptive, empirically-derived consensus classification. The recent shift towards personalized medicine has resulted in an increased demand for precise, mechanism-based diagnoses, which is not fully met by the contemporary transplantation pathology standard of care. The expectation is that molecular techniques will provide novel pathogenetic insights that will allow for the identification of more accurate diagnostic, prognostic, and therapeutic targets. Here we review the current state of molecular renal transplantation pathology. Despite significant research activity and progress within the field, routine adoption of clinical molecular testing has not yet been achieved. The recent development of novel molecular platforms suitable for use with formalin-fixed paraffin-embedded tissue will offer potential solution for the major barriers to implementation. The recent incorporation of molecular diagnostic criteria into the 2013 Banff classification is a reflection of progress made and future directions in the area of molecular transplantation pathology. Transcripts related to endothelial injury and NK cell activation have consistently been shown to be associated with antibody-mediated rejection. Prospective multicenter validation and implementation of molecular diagnostics for major entities remains an unmet clinical need in transplantation. It is expected that an integrated system of transplantation pathology diagnosis comprising molecular, morphological, serological, and clinical variables will ultimately provide the greatest diagnostic precision.

Molecular diagnostics in renal allograft biopsy interpretation: potential and pitfalls

Application of molecular techniques, particularly gene expression microarrays, to the study of T cell-mediated rejection, antibody-mediated rejection (ABMR), and other changes in renal allografts has grown. While studies of gene expression within renal allograft biopsies have elucidated the pathogenesis of rejection and helped lead to recognition of C4d-negative ABMR, the use of molecular studies to achieve greater diagnostic accuracy and precision, guide therapy, and decrease the need for biopsies still remains a hope for the future.

Transitional B lymphocytes are associated with protection from kidney allograft rejection: a prospective study

Recent cross-sectional studies suggest an important role for transitional B lymphocytes (CD19 + CD24hiCD38hi) in promoting transplant tolerance, and protecting from late antibody-mediated rejection (ABMR). However, prospective studies are lacking. This study enrolled 73 de novo transplant recipients, and collected serial clinical, immunological and biochemical information over 48 ± 6 months. Cell phenotyping was conducted immediately prior to transplantation, and then on five occasions during the first year posttransplantation. When modeled as a time-dependent covariate, transitional B cell frequencies (but not total B cells or "regulatory" T cells) were associated with protection from acute rejection (any Banff grade; HR: 0.60; 95% CI: 0.37-0.95; p = 0.03). No association between transitional B cell proportions and either de novo donor-specific or nondonor-specific antibody (dnDSA; dnNDSA) formation was evident, although preserved transitional B cell proportions were associated with reduced rejection rates in those patients developing dnDSA. Three episodes of ABMR occurred, all in the context of nonadherence, and all associated with in vitro anti-HLA T cell responses in an ELISPOT assay (p = 0.008 versus antibody-positive patients not experiencing ABMR). This prospective study supports the potential relevance of transitional ("regulatory") B cells as a biomarker and therapeutic intervention in transplantation, and highlights relationships between humoral immunity, cellular immunity and nonadherence.

A pathogenesis-based transcript signature in donor-specific antibody-positive kidney transplant patients with normal biopsies

Affymetrix Human Gene 1.0-ST arrays were used to assess the gene expression profiles of kidney transplant patients who presented with donor-specific antibodies (DSAs) but showed normal biopsy histopathology and did not develop antibody-mediated rejection (AMR). Biopsy and whole-blood profiles for these DSA-positive, AMR-negative (DSA +/AMR-) patients were compared to both DSA-positive, AMR-positive (DSA +/AMR +) patients as well as DSA-negative (DSA -) controls. While individual gene expression changes across sample groups were relatively subtle, gene-set enrichment analysis using previously identified pathogenesis-based transcripts (PBTs) identified a clear molecular signature involving increased rejection-associated transcripts in AMR - patients. Results from this study have been published in Kidney International (Hayde et al., 2014 [1]) and the associated data have been deposited in the GEO archive and are accessible via the following link: http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE50084.